Upcasting is a well known technique wherein a cooled mold, disposed within a molten body of metal, is vertically oscillated to form a continuous cast product. Examples of upcasting may be found in U.S. Pat. Nos. 4,301,857; 4,307,770 and 4,211,270.
Most commercial applications employing upcasting methodology utilize copper or copper-base alloys (brasses, bronzes). Since these materials are relatively easy to melt and usually have straightforward chemical compositions they lend themselves to expeditious large scale continuous melting and forming operations.
Generally speaking the metal is melted in at least one separate furnace that may also serve as a holding facility. The molten metal is then transferred by a ladle or a tundish system to the casting furnace. The caster is partially submerged into the melt and oscillated to generate the desired product.
A concern in any continuous casting operation is the ability to maintain the specification chemistry from the beginning of the cast to the end. Casting times may be long and external heating of the ladle is needed to maintain the necessary temperatures. It has been found that minor elements, particularly reactive elements, can fade over time and the bath may become oxidizing thereby producing a gassy product.
Since the demand for copper containing products is great, these problems can be overcome. Large quantities of copper are continuously melted and fed to the casters.
In contrast, the commercial quantities of nickel and nickel-base alloy materials fashioned into continuous cast rod and the like are small by comparison. Accordingly, a continuous caster for working them must be in reality a semi-continuous or batch operation. Moreover, the caster must be amenable to quick changes in alloy chemistry and size requirements while maintaining strict compositional limits and complete deoxidation throughout the melting and casting operations. Oftentimes, the chemistry of nickel-base alloy systems is more critical than copper-base alloys. This requires greater vigilance during processing.
In essence, in order to employ an upcaster efficiently with respect to nickel and nickel-base alloys, the technique requires:
1) the capacity to provide molten metal to the upcaster on a continuous or semi-continuous (batch) basis;
2) the ability to quickly handle substantial alloy changes; and
3) the availability of a "clean" furnace for each different alloy or alloy family.